1. Field of the Invention
The present invention generally relates to a cap for a writing device and particularly to a protective cap for a writing device utilizing aqueous ink.
2. Background of the Invention
Cap of conventional writing device using aqueous ink typically has an inner cap which is made of soft material. Thus, when the writing device is coupled with the cap, the inner cap is abutted against the leading end of the writing device so as to prevent drying of the ink. However, during the process of coupling of the writing device with the cap, air within the cap is compressed--thereby increasing the internal pressure of the cap. When the cap is detached from the writing device, the air pressure within the cap is abruptly decreased--resulting in the ink in the writing tip of the writing device being forcibly discharged and evaporated. As the cap is alternately coupled and detached with and from the writing device during its normal use, a significant amount of the ink is wasted in a given pen during its given lifetime.
The prior art discloses cap with writing instruments of various designs and means.
U.S. Pat. No. 5,336,011 to Ferguson et al. discloses a storage cap with spring biased female threads for a rod-shaped device or instrument, particularly a fountain pen, wherein the female threads for securing the device within the cap are disposed within an axially and rotationally moveable ring.
U.S. Pat. No. 5,176,460 to Garry discloses a pen cap for a writing instrument barrel comprising a chamber defining inner housing adapted to snugly receive a reduced nib carrying portion of the barrel and a spaced flow-through outer housing coextensive at the proximal end thereof with the inner housing to define a narrow passage therebetween with spaced radially extending rib members extending thereacross between the spaced inner and outer housing to strengthen the pen cap at the proximal end thereof.
U.S. Pat. No. 5,154,526 to Bothe discloses a protective cap for capillary writing instruments comprised of a relatively flexible outer casing and a relatively rigid inner casing. One end of outer casing is adapted to form a substantially fluid tight seal on the body of a writing instrument. A flexible sealing means, e.g., spherical, is positioned between the inner sheath and the outer sheath so as to form a substantially fluid tight seal on the tip of a writing instrument inserted into the inner casing and placed in contact with the sealing means.
Although these prior arts disclose caps for writing instruments of various designs and means, none of them disclose a cap for writing device of the particular structure and novelty as disclosed and claimed hereinafter.
It is thus a primary objective of the present invention to provide a cap for writing device which prevents sudden pressure variations within the cap.
Another objective of the present invention is to provide a cap for writing device which prevents drying of ink of the writing device.
Yet another objective of the present invention is to provide a cap for writing device which prevents evaporation-drying of ink of the writing device.